1. Field of the Invention
The present invention relates to a substrate processing method of performing sequential processes from a predetermined wet process to a drying process on a variety of substrates such as semiconductor wafers, glass substrates for photomask, glass substrates for liquid crystal display, glass substrates for plasma display, optical disk substrates (hereinafter, simply referred to as “substrate”), as well as to a substrate processing apparatus and a substrate processing system suited for such a method.
2. Description of the Related Art
In recent years, the semiconductor devices have been speeding toward fine structure which has raised new problems in the substrate processing field. In a case where a fine pattern is formed by patterning a resist applied on a substrate, for example, a wet developing process and a drying process are performed in this order. In the wet developing process for developing the resist applied on the substrate, an alkaline developing process and a rinsing process are carried out, for example. Specifically, the alkaline developing process uses an aqueous alkaline solution for removal of unwanted resist, whereas the rinsing process uses a rinse liquid such as pure water for removal of the aqueous alkaline solution (for terminating the developing process). In the drying process, on the other hand, the substrate is rotated thereby subjecting the rinse liquid remaining on the substrate to centrifugal force for removing the rinse liquid. Thus is dried the substrate (spin drying). In the drying process, the substrate encounters the appearance of interface between the rinse liquid on the substrate and gas as the drying process proceeds. When such an interface appears in a gap between fine pattern portions of a semiconductor device, the fine pattern portions are drawn toward each other by the surface tension of the rinse liquid so that the fine pattern portions are collapsed.
In addition, fluid resistance produced in the spin drainage of the rinse liquid, pressure acting to discharge the rinse liquid from the fine pattern portions, and the air resistance and centrifugal force associated with the high-speed rotation in excess of 3000 rpm are thought to be involved in the collapse of the fine pattern portions.
As a solution to this problem, there has been proposed a supercritical drying process wherein the substrate is retained in a pressure container while a supercritical fluid having properties of low viscosity, high diffusivity and no surface tension (hereinafter, referred to as “SCF”) is introduced into the pressure container for accomplishing the supercritical drying of the substrate.
For instance, an apparatus described in Japanese Unexamined Patent Publication No. 2000-223467 (hereinafter, referred to as “Patent Document 1”) is adapted to retain, in a reaction chamber, a substrate subjected to the developing process (alkaline developing process and rinsing process). With the substrate retained in the reaction chamber, the apparatus activates a pump unit to pump a given amount of liquefied carbon dioxide from a cylinder into the reaction chamber. In the meantime, the pressure of carbon dioxide in the reaction chamber is automatically controlled by way of a pressure control valve so as to be maintained in the range of 7.38 to 8 MPa whereby the carbon dioxide in the reaction chamber is transformed to the supercritical fluid. Subsequently, the supercritical fluid is released from the reaction chamber to reduce the pressure in the reaction chamber, whereby the substrate is allowed to dry.
The supercritical drying apparatus is dedicated solely to the drying process and hence, the developing process (alkaline developing process and rinsing process) is carried out in a developing apparatus separate from the drying apparatus. In order to subject the substrate to the sequential substrate processes from the developing process to the drying process, the conventional practice requires the substrate wet with the rinse liquid to be transported to the supercritical drying apparatus after the performance of the alkaline developing process and rinsing process in the developing apparatus. This is because if the substrate becomes air-dry during the transportation from the developing apparatus to the supercritical drying apparatus, the fine pattern portions are drawn toward each other by the surface tension of the rinse liquid so as to be collapsed. As a consequence, the performance of the supercritical drying means nothing.
As a solution, it may be contemplated to provide a developing unit functioning as the developing apparatus and a high-pressure processing unit functioning as the supercritical drying apparatus in the same apparatus, which is further provided with a transport robot as a transport unit which may wet-transport the substrate developed by the developing unit to the high-pressure processing unit.
Unfortunately, the aforesaid substrate processing apparatus including the developing unit, the high-pressure processing unit and the transport robot takes only the alkaline developing process into consideration, thus suffering poor versatility. The developing process taken in the fabrication process for fabricating electronic components such as used in semiconductor apparatuses and liquid crystal display units is not limited to the aforesaid alkaline developing process but includes a plurality of developing processes. In cases, for example, in place of the alkaline developing solution, an organic developing solution such as butyl acetate may be used according to a film material for forming a resist film. The developing process using the organic developing solution may be followed by the rinsing process using isopropyl alcohol (IPA) as the rinse liquid.
In order to enhance the versatility of the substrate processing apparatus, it may be contemplated to provide the processing apparatus not only with the alkaline developing unit, an alkaline-development transport robot for transporting an alkaline developed substrate and a high-pressure processing unit which carry out the alkaline developing process, but also with an organic developing unit for performing an organic developing process, an organic-development transport robot for transporting an organically developed substrate and a high-pressure processing unit which carry out the organic developing process. However, such a substrate processing apparatus provided with the special transport units (the alkaline-development transport robot and the organic-development transport robot) corresponding to the individual developing contents is detrimentally increased in size and costs.
On the other hand, a substrate processing apparatus has been proposed which is designed to perform a wet process such as the developing process and a high-pressure drying process using the SCF in the same reactor. According to an apparatus disclosed in Japanese Unexamined Patent Publication No. 11-87306 (hereinafter, referred to as “Patent Document 2”), for example, when a processing fluid, such as a rinse liquid, an etching solution or a developing solution, is introduced from a liquid tank into the reactor with a substrate set at place therein, the processing fluid in the reactor is stirred by a rotating mechanism so that a smooth and consistent wet process is effected. Subsequently, a rinse liquid in place of the processing solution is introduced from a liquid tank into the reactor for carrying out the rinsing process. Thereafter, the rinse liquid is discharged from the reactor while the SCF from a gas cylinder is introduced into the reactor. Thus, the rinse liquid is replaced with the SCF. Then, the SCF is slowly discharged for carrying out the supercritical drying process or the high-pressure drying process. That is, this substrate processing apparatus negates the need for transporting the substrate from the developing apparatus to the supercritical drying apparatus. Therefore, there occurs no problem that the substrate becomes air-dry during the transportation so that the fine pattern portions are collapsed as drawn toward each other by the surface tension of the rinse liquid.
However, the following problem is encountered by the conventional apparatus wherein the wet process and the high-pressure drying process are sequentially performed in a single reactor. Specifically, the substrate processing apparatus designed to perform the high-pressure drying process has more limiting conditions than the conventional substrate processing apparatus widely used in the art or the substrate processing apparatus carrying out surface treatment under normal pressures. The most crucial one of the limiting conditions is that the range of selection of the processing fluid is limited. The reason is as follows. This substrate processing apparatus must employ a pressure container as the reactor. Where a corrosive processing fluid of strong acid or strong alkali is used for carrying out the surface treatment, the processing fluid corrodes a liquid contacting surface of the pressure container. On this account, a corrosive chemical agent of strong acid or alkali cannot be introduced in the pressure container for carrying out the surface treatment. As a result, the range of selection of the processing fluid is notably reduced.
It may naturally be contemplated to apply an anti-corrosive coating such as of a fluorine resin to an inside surface of the pressure container for the purpose of eliminating the above limitation. However, it is actually impossible to ensure that the anti-corrosive coating continues to exhibit its function over an extended period of time under the high pressure condition. Even if the inside surface of the pressure container is coated with the anti-corrosive coating, it is impracticable to apply the anti-corrosive coating on the inside surfaces of all the associated components including thin piping extended to the pressure container, joints, high-pressure valves and the like.